1. Technical Field
The present invention relates to a filter for an air bag inflator.
2. Description of the Prior Art
Inflators to expand an air bag, when a vehicle encounters sudden deceleration, such as in a collision, are well known. The inflated air bag restrains movement of an occupant of the vehicle during the collision. The air bag is inflated by gas generated through ignition of gas generating material. The gas generating material is contained in the air bag inflator.
A commonly used gas generating composition is one containing an alkali metal azide and a metal oxide, such as copper oxide or iron oxide. The composition may also contain an oxidizing agent such as sodium nitrate or ammonium perchlorate. Ignition of the gas generating composition produces a hot gas stream. The hot gas stream will typically include nitrogen gas, oxygen, molten metal, sodium oxide, a sodium salt of the metal, and metal nitride. The nitrogen gas carries the other reaction products, some of which are in the form of a residue or sinter. It is desirable to remove certain reaction products from the nitrogen gas stream before the gas streams enters the air bag.
U.S. Pat. No. 4,878,690 discloses a filter assembly used in a gas generator for a vehicle occupant restraint. The filter assembly comprises, in the direction of gas flow, a plurality of layers of 30 mesh stainless steel screen, a filter member for fine filtering the generated gas, and then another layer of 30 mesh stainless steel screen. The filter member can be an alumina-silica fiber paper such as "Lytherm" ceramic fiber paper marketed by Mansville Co. Other examples of filter paper disclosed in the patent are silica fiber paper marketed by Sandtex Corporation of Japan under the trademark "Sandtex" and a filter material sold by National Standard Corp. of Corbin, Ky. under the trademark "FIBREX".
U.S. Pat. No. 4,902,036 discloses a gas generator for a vehicle occupant restraint. The generator contains a plurality of filters including a final filter assembly which filters the nitrogen gas before the gas exits from the generator into an air bag. The final filter assembly comprises a first section of mesh screens. The mesh screens remove particulate reaction products from the gas stream. The final filter also has a second section of screens of smaller mesh size. The screen sections are separated by a pad formed from a ceramic fiber that is a mixture of aluminum oxide and silicon dioxide. The pad is sold under the trademark "Fiberfrax" by Sohio Carborundum, Inc.